The present invention relates to the field of electronic circuits, and, more particularly, to circuit cards.
The electronic components of computers and other modern electronic devices are frequently mounted on a printed wiring board (PWB). The PWB and electronic components mounted thereon define a circuit card that can be inserted into a chassis and electronically coupled to a backplane of the electronic device. One circuit card may serve as a host card to another circuit card electrically and physically connected thereto. The circuit card connected to the host circuit card is typically carried in piggyback fashion above and parallel to the host circuit card and is conventionally referred to as a mezzanine circuit card.
Commercial off-the-shelf mezzanine circuit cards are increasingly used for a variety of functions. A peripheral component interconnect (PCI) mezzanine card, for example, provides an efficient network interface allowing multiple computers and/or other electronic devices to electronically communicate and exchange data with one another. A particular example of such a mezzanine card is a fiber channel (FC) network interface card (NIC) that is mounted to a host card that can be used, for example, in the avionics field.
As with electronic devices generally, operation of a circuit card can generate heat that, if not adequately controlled through some cooling mechanism, may cause damage to the electronic components carried on the circuit cards. One approach has been to use convection cooling techniques and devices. With convection cooling, the circuit cards may be mounted to a chassis in a way that permits cooling air to flow over the circuit cards.
For proper convection cooling, an adequate flow of cooling air should be generated. This may be done, for example, using a fan encased in the electronic device. The circuit cards, moreover, should be arranged so that a sufficient amount of the circuit card""s surface area is exposed to the cooling air, and so that the cooling air flows relatively freely within the electronic device. Such arrangements may be incompatible, however, with some uses of circuit cards where electronic devices typically need to be quite small in size. Accordingly, there may not be space in such devices for a fan or to arrange the circuit cards so that air flows freely over them.
Accordingly, there is increasing demand for mezzanine and other circuit cards that can be conduction cooled. This increased demand is evinced, for example, by the Conduction Cooled PCI Mezzanine Card (CCPMC) Draft Standard VITA 20-200x (Draft 1.16) released in July of 2001 by the VITA Standards Organization. There is also a need to make conduction cooling more effective so that circuit cards can be used in environments subject to extreme temperature ranges, such as for military applications and in avionics.
U.S. Pat. No. 6,212,075 to Habing et al. discloses a kit for adapting circuit cards to increase their cooling efficiency while allowing them to remain compliant with IEEE 1101.2 specifications. The kit includes an extended width wedgelock that connects a frame to the cold wall of a card chassis. The frame, in turn, connects to a base card and a mezzanine card carried thereon. Heat is transferred via the frame from the cards and from a component-mounted thermal heat sink to the cold wall. The wedgelock has an extended width so as to increase the surface area contact between the frame and the cold wall.
With conventional conduction cooling techniques and devices for host and mezzanine circuit cards, heat is conducted from both the host circuit card and the mezzanine circuit card carried thereon to a single heat sink. Thus heat is conducted additively from both circuit cards to the single heat sink, which, in turn, may connect to the cold wall of the chassis to conduct the combined heat in serial fashion to the cold wall.
Attempts to provide better cooling of circuit card devices have not been wholly satisfactory. For example, thermoelectric cooling may require a relatively large amount of power, while another techniquexe2x80x94that of conducting heat via heatpipesxe2x80x94does do not appear suited for robust environments such as those associated with military avionics. Moreover, standards such as the Conduction Cooled PCI Mezzanine Card (CCPMC) Draft Standard may be difficult to conform to using such conventional approaches.